The present invention relates to an optical disk drive selectively operable with different kinds of optical disks and, more particularly, to an objective lens actuator assembly advantageously applicable to such an optical disk drive.
An objective lens actuator assembly for the above application is disclosed in "Development of Twin Lens Optical Pick-up for DVD", Technical Report, the Institute of Television Engineers of Japan, 1995, Vol. 46 (VIR95-46), pp. 53-60, and "Switching VD/CD Lenses", Nikkei Mechanical, Aug. 7, 1995, Vol. 460, pp. 62-65. The actuator assembly is built in an optical disk drive selectively operable with a CD (Compact Disk) or a DVD (Digital Video Disk), as desired. While CDs and DVDs share the same principle of playing, they are different in specifications including thickness. To allow a single optical disk drive to read information out of the two different kinds of optical disks, it is necessary to provide the disk drive with two different kinds of objective lenses (one for converging a laser beam issuing from a light source onto a CD and the other for converging it onto a DVD).
In the above conventional actuator assembly, two objective lenses assigned to DVDs and CDs, respectively, are mounted on a disk-like lens holder. The lens holder is rotatable about a shaft and movable back and forth in the direction parallel to the shaft. The actuator assembly includes a tracking actuator, a focusing actuator, and an operation control circuit. The focusing actuator causes the lens holder to move in the direction parallel to the shaft. The tracking actuator has a plurality of tracking coils mounted on the lens holder and causes the lens holder to rotate about the shaft for thereby positioning the objective lenses. The tracking actuator is capable of correcting a tracking error and replacing the objective lens at the same time.
However, the conventional actuator assembly has some issues yet to be solved, as follows. The tracking coils must be mounted on the lens holder in accordance with the number of objective lenses, increasing the overall weight of the lens holder. As a result, power consumption by the tracking actuator is increased, and the operation speed is lowered. Moreover, control for the tracking error correction and lens replacement must be executed with each of the two pairs of tracking coils, resulting in the need for two pairs of operation control circuits and two pairs of tracking coil switching circuits. This undesirably complicates the configuration of the overall operation control circuitry.